In forming damascene structures in integrated circuit manufacturing processes, the surface condition of the damascene opening is critical for achieving acceptable adhesion and coverage of overlying layers. The damascene opening, for example a dual damascene opening is formed in an inter-metal dielectric (IMD) insulating layer by a series of photolithographic patterning and etching processes, followed by formation of a barrier layer and overlying metal, e.g., copper, seed layer to promote a copper electro-chemical plating (ECP) deposition process.
Increasingly, low-K IMD layers are required to reduce signal delay and power loss effects as integrated circuit devices are scaled down. One way this has been accomplished has been to introduce porosity or dopants into the IMD layer. In particular, incorporation of low-K materials with dielectric constants less than about 3.5 has become standard practice as semiconductor feature sizes have diminished to less than 0.2 microns. As feature sizes decrease below about 0.13 microns, for example including 90 nm and 65 nm critical dimension technology materials with dielectric constants less than about 2.5 will be required. In addition, the aspect ratios (height/width) of interconnect openings becomes increasingly large, making continuous coverage of physical vapor deposition (PVD) process more problematical. The phenomena of increasingly porous IMD surfaces and increasingly high aspect ratio openings, either individually or in combination, have created manufacturing limitations that must be overcome to form reliable copper damascenes in smaller critical dimension technologies.
For example, the presence of a relatively rough surface due to the penetration of pore openings at the surface of an opening etched into a low-K IMD layer produces surface micro-openings adversely affecting coverage of overlying deposited layers, for example diffusion barrier layers and seed layers. As a result, thicker barrier layers, with increased series resistance are required in order to avoid forming barrier layers having pinholes which undesirably allow electromigration of metal into the IMD layer. Further, the deposition of seed layers, typically formed by PVD processes, may be non-continuously formed, thereby adversely affecting eletro-chemical deposition processes. For example, non-contiguous seed layers, for example, including as pin holes, can cause the formation of voids within the copper filling portion of an ECP deposited copper layer.
Another problem with PVD copper seed layers is the ready formation of copper oxides over portions of the seed layer surface prior to carrying out the ECP process, further contributing to the formation of voids in the ECP deposited copper layer due to variable deposition rates caused by variable conductivities of the seed layer.
There is therefore a need in the integrated circuit manufacturing art to develop an improved copper seed layer and method of forming the same to improve a copper ECP process to improve performance and reliability of copper damascenes.
It is therefore among the objects of the present invention to provide an improved copper seed layer and method of forming the same to improve a copper ECP process to improve performance and reliability of copper damascenes, while overcoming other shortcomings of the prior art.